The treatment of wastewater to reduce effluents and recycle usable water is a matter of the utmost importance to the overall effort of reducing pollution and conserving water. A particular area of concern is the handling of graywater aboard ships and boats, e.g., marine graywater. Graywater is defined as the combined effluent wastewaters from shipboard galleys, sculleries, dishwashers, laundries, showers, sinks, and wash basins (including deep sinks in work areas such as machine shops and medical areas). The contaminants are typically food particles of up to substantial dimensions (e.g., food slices), animal fats, vegetable oils, soaps, detergents, body oils, human hairs, metallic particles from sculleries and machine shops, solvents, and small articles of clothing (e.g., socks) which may have snaked their way through the laundry system. Graywater is usually differentiated both from blackwater, which is a salt-water-based collection of body wastes and paper materials from shipboard head spaces, and from bilgewater, which is a salt-water-based accumulation of all other shipboard wastewater and which may contain chemical solvents and the like.
Although highly variable in its rate of generation, as well as the concentration and type of contaminants, graywater is generated at an average rate of approximately 5-20 gallons per man per day on board ship. Thus, for example, graywater generation can be on the order of 4,000 gal/day for a naval frigate with a crew of 200 to as high as 120,000 gal/day for an aircraft carrier with a crew of 6,000. Average flow rates of graywater on board such ships can range from about 2.8 gal/min to about 83.3 gal/min, with peak flow rates ranging from about 8.4 gal/min to about 250 gal/min.
Conventional coalescers and centrifugal separators are inadequate to treat and purify graywater, since, for example, the viscosities and surface tensions of soaps and water are too close to permit satisfactory separation. Many ships directly discharge graywater, without treatment, into navigable waters, including lakes and waters near the shoreline. Some ships are equipped with concentration, holding, and transfer tanks for the purpose of storing graywater until it can be pumped to a dockside sanitation system. These ships utilize the concentration, holding, and transfer tanks in an attempt to avoid graywater discharges into lakes and waters near the shoreline, but routinely discharge graywater into the high seas or, when the tanks are filled to capacity, other navigable waters. In those increasingly larger areas where graywater discharge is prohibited, expensive and cumbersome means, such as the off-loading of stored graywater onto tankers, are utilized, or else the prohibitions are merely ignored.
There remains a need, therefore, for an effective and economical means to reduce wastewater effluent, particularly graywater discharges from ships. It is an object of the present invention to provide such a treatment means. It is another object of the present invention to concentrate wastewater contaminants to render them more amenable to storage and disposal while allowing for the discharge of purified water recovered from the wastewater. It is also an object of the present invention to provide a means of treating wastewater, particularly graywater, so as to recycle usable water and thereby conserve water. These and other objects and advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.